(1) Field of the Invention
The invention is related to an aerodynamic, blunt aft body, particularly an aerodynamic, blunt aft body of a helicopter with a rear loading capability according to the preamble of claim 1. The upsweep angle of the rear part of the helicopter fuselage is defined by the angle between the lowest tangential z-plane of the fuselage midsection and the tangential planes with the fuselage midsection. An aft body is blunt, when the maximum of the said upsweep angle is greater than 25°.
(2) Description of Related Art
The aerodynamics of helicopters with fuselages featuring a blunt aft body, e.g. fuselages featuring a backdoor or a ramp/hatch with rear loading capabilities, are characterized by flow separation in the blunt aft body region, said flow separation being the main source of fuselage drag. Improving the flow by reducing as much as possible the separation region on the blunt aft body to weaken the turbulence in this region, can noticeably reduce drag of the aircraft and hence required power and fuel consumption of the helicopter can be reduced.
The installation of so called strakes is known to reduce the drag of cambered rear loading aft bodies of airplanes. However, helicopters do indeed fly often at flow conditions with side-slip angles much higher than the ones airplanes experience. For those high side-slip angles the flow separates upstream of the strakes. In these cases, the fuselage drag is no longer reduced, but can even increase.
The document US 2009/0078830 A (Airbus) discloses a surface including a geometrical deformation configured to generate lateral aerodynamic disturbances on the central fairing to control the flow of air. This patent does neither deal with helicopters nor with reducing separated flows, nor with lateral stability.
The document U.S. Pat. No. 4,786,009 A (NASA) discloses a method and apparatus for controlling yaw and pitch at high angles of attack by controlling the vortex pattern around the forebodies of air vehicles by means of deflecting strakes. This patent does not deal with drag reduction of blunt aft bodies. In fact these deflecting strakes generate control moments around the pitch and yaw axis by increasing the fuselage sectional forebody drag. Considering the local flow condition around the fuselage forebody the strakes act as spoilers, being placed transversally with respect to the air flow.
The document U.S. Pat. No. 5,209,430 A discloses the use of strakes on helicopters to spoil the airflow on the tail boom so that less side thrust is needed from the tail rotor. It is not dealing with blunt fuselages.
The document U.S. Pat. No. 7,686,245 discloses a download alleviation strake on a rotary aircraft said strake extending at least partially along a length of the fuselage and configured to reduce a downwash download during operation of the rotor assembly. There is no hint to drag reduction or lateral stability.